Novel cyanine dyes with pyrroloquin-oxaline or pyrrolopyrazine nuclei

ABSTRACT

CYANINE DYES WHICH FEATURE A PYRROLO(2,3-B)QUINOXALINE NUCLEUS OR A PYRROLO(2,3-B)PYRAZINE NUCLEUS, JOINED AT THE 3-CARBON ATOM THEREOF TO THE METHINE LINKAGE OF THE CYANINE DYE, SENSITIZE PHOTOGRAPHIC SILVER HALIDE EMULSIONS.

United States Patent Olhce 3,736,321 Patented May 29, 1973 3,736,321 NOVEL CYANINE DYES WITH PYRROLOQUIN- OXALINE OR PYRROLOPYRAZINE NUCLEI John D. Mee, Donald W. Heseltine, and Wilbur S. Gaugh,

Rochester, N.Y., assignors to Eastman Kodak Company, Rochester, N.Y.

No Drawing. Original application Feb. 15, 1968, Ser. No. 705,595, now Patent No. 3,598,595. Divided and this application June 22, 1970, Ser. No. 59,815

Int. Cl. C09b 23/06, 23/10 US. Cl. 260-240.6 6 Claims ABSTRACT OF THE DISCLOSURE Cyanine dyes which feature a pyrrolo[2,3-b] quinoxaline nucleus or a pyrrolo[2,3-b]pyrazine nucleus, joined at the 3-carbon atom thereof to the methine linkage of the cyanine dye, sensitize photographic silver halide emulsions.

This application is a division of our copending application Ser. No. 705,595 filed Feb. 15, 1968, now US. Pat. 3,598,595.

This invention relates to novel cyanine dyes and novel photographic emulsions containing such dyes. The novel dyes of this invention are especially useful as electron acceptors and spectral sensitizers for direct positive photographic silver halide emulsions.

It is known that direct positive images can be obtained with certain types of photographic silver halide emulsions. For example, photographic emulsions have been proposed for this purpose comprising an electron acceptor and silver halide grains that have been fogged with a combination of a reducing agent and a compound of a metal more electropositive than silver. One of the advantages of such direct positive emulsions it that the high-light areas of the images obtained with these materials are substantially free from fog. However, known materials of this type have not exhibited the high speed required for many applications of photography. Also, such known materials have not shown the desired selective sensitivity, especially to radiation in the green to red region of the spectrum. It is evident, therefore, that there is need in the art for improved direct positive photographic materials having both good speed and desirable sensitivity to longer wavelength radiations.

It is, accordingly, an object of this invention to provide a new class of cyanine dyes. Another object of this invention is to provide novel cyanine dyes which function as effective electron acceptors and spectral sensitizers in photographic silver halide emulsions. A further object of this invention is to provide novel photographic silver halide emulsions, including direct positive photographic emulsions, containing one or more of the novel dyes of the invention. Another object of this invention is to provide photographic emulsions containing novel cyanine dyes and a photographic color former. Still another object of this invention is to provide photographic elements comprising a support having thereon at least one layer of the novel emulsions of the invention. Other objects of this invention will be apparent from this disclosure and the appended claims.

We have now found that certain cyanine dyes derived from l-substituted pyrrolo[2,3-b]pyrazines and l-substituted pyrrolo[2,3-'b]quinoxalines are outstanding electron acceptors and spectral sensitizers for direct positive type of photographic silver halide emulsions. They provide superior reversal systems, especially with fogged silver halide emulsions, that are characterized by both good speed and desired selective sensitivity to radiation in the green to red region of the spectrum with maximum sensitivity occurring in most cases in the region of about 500- 600 nm. The images produced with these new direct positive emulsions are clear and sharp and of excellent contrast.

The novel cyanine dyes of the invention comprise first and second 5- to 6-membered nitrogen containing heterocyclic nuclei joined together by a methine linkage containing from 2 to 3 carbon atoms in the methine chain (including those linkages wherein a methine group is substituted by alkyl, aryl or heterocyclic substituents); the first of said nuclei being selected from a pyrrolo[2,3-b] quinoxaline nucleus or a pyrrolo[2,3-b]pyrazine nucleus joined in each case at the 3-carbon atom thereof to said linkage; and, said second nucleus being selected from (a) a heterocyclic nitrogen containing nucleus of the type used in the production of cyanine dyes, when said linkage is a dimethine linkage, and (b) when said linkage is a trimethine linkage, said second nucleus is selected from the group consisting of a 2-arylindole nucleus, a pyrrolo- [2,3-b]quinoxaline nucleus and a pyrrolo[2,3-'b]pyrazine nucleus, each of said nuclei being joined at the 3-carbon atom thereof to said trimethine linkage. Preferably, the second nucleus is a desensitizing nucleus.

The preferred class of novel cyanine dyes of the invention include those represented by the following general formula:

I. Rs

wherein n represents a positive integer of from 1 to 2; L represents a methine linkage, e.g., -CH=,

C(2-pyridyl)=; -C(2-thienyl)-=; etc.; R represents an alkyl group, including substituted alkyl (preferably a lower alkyl containing from 1 to 4 carbon atoms), e.g., methyl, ethyl, propyl, isopropyl, butyl, hexyl, cyclohexyl, decyl, dodecyl, etc., and substituted alkyl groups (preferably a substituted lower alkyl containing from 1 to 4 carbon atoms), such as a hydroxyl group, e.g., fl-hydroxyethyl, w-hydroxybutyl, etc., an alkoxyalkyl group, e.g., fJ-methoxyethyl, w-butoxybutyl, etc., a carboxyalkyl group, e.g., p-carboxyethyl, w-carboxybutyl, etc., a sulfoalkyl group, e.g., fi-sulfoethyl, w-sulfobutyl, etc., a sulfatoalkyl group, e.g., B-sulfatoethyl, w-sulfatobutyl, etc., an acyloxyalkyl group, e.g., p-acetoxyethyl, -acetoxypropyl, w-butyryloxybutyl, etc., an alkoxycarbonylalkyl group, e.g., ,B-methoxycarbonylethyl, w-ethoxycarbonylbutyl, etc., or an aralkyl group, e.g., benzyl, phenethyl, etc.; an alkenyl group, e.g., allyl, l-propenyl, 2-butenyl, etc.; or, an aryl group, eg., phenyl, tolyl, naphthyl, methoxyphenyl, chlorophenyl, etc.; R represents an alkyl group, e. g., methyl, ethyl, propyl, isopropyl, butyl, decyl, dodecyl, etc., or an aryl group, e.g., phenyl, tolyl, naphthyl, etc.; R and R each represents a hydrogen atom, an alkyl group (preferably a lower alkyl containing from 1 to 4 carbon atoms), e.g., methyl, ethyl, propyl, isopropyl, butyl, hexyl, cyclohexyl, decyl, dodecyl, etc., or an aryl group, e.g., phenyl, tolyl, naphthyl, chlorophenyl, nitrophenyl, methoxyphenyl, etc.; and, R and R taken together can represent the non-metallic atoms necessary to complete a pyrrolo[2,3-b]quinoxaline nucleus; R represents a hydrogen atom or an aryl group, e.g., phenyl, tolyl, naphthyl, chlorophenyl, nitrophenyl, methoxyphenyl, etc.; X represents an acid anion, e.g., chloride, bromide, iodide, thiocyanate, sulfamate, perchlorate, p-toluenesulfonate, methyl sulfate, ethyl sulfate, etc.; and Z represents 3 the non-metallic atoms necessary to complete a heterocyclic nucleus of the type used in cyanine dyes, and prefera'bly a desensitizing nucleus, containing from to 6 atoms in the heterocyclic ring, which nucleus may contain a second hetero atom such as oxygen, sulfur, selenium or nitrogen, such as the following nuclei:

a thiazole nucleus, e.g., thiazole, 4-methylthiazole, 4- phenylthiazole, S-methylthiazole, 5-phenylthiazole, 4,5- dimethylthiazole, 4,5-diphenylthiazole, 4 (2 thienyl) thiazole, benzothiazole, 4-chlorobenzothiazole, 4- or S-nitrobenzothiazole, S-chlorobenzothiazole, 6-chlorobenzothiazole, 7-chlorobenzothiazole, 4-methylbenzothiazole, S-methylbenzothiazole, G-methylbenzothiazole, 6-nitrobenzothiazole, '5-bromobenzothiazo1e, -brornobenzothiazole, S-chloro-6-nitrobenzothiazole, 4-phenylbenzothiazole, 4-methoxybenzothiazole, S-methoxybenzothiazole, G-methoxybenzothiazole, S-iodobenzothiazole, 6-iodobenzothiazole, 4-ethoxybenzothiazole, 5- ethoxybenzothiazole, tetrahydrobenzothiazole, 5,6-dimethoxybenzothiazole, 5,6-dioxymethylenebenzothiazole, S-hydroxybenzothiazole, 6-hydroxybenzothiazole, naphtho[2,1-d]thiazole, naphtho[l,2-d]thiazole, naphtho[2,3-d] thiazole, S-methoxynaphtho[2,3-d] thiazole, 5-ethoxynaphtho[ 1,2-d] thiazole, S-methoxynaphthm [2,l-d]thiazole, 7-methoxynaphtho[2,1-d]thiazole, 4'- methoXythianaphtheno-7,'6'-4,5-thiazole, nitro group substituted n-aphthothiazoles, etc.;

an oxazole nucleus, e.g., 4-methyloxazole, 4-nitro-oxazole, S-methyloxazole, 4-phenyloxazole, 4,5-diphenyloxazole, 4-ethyloxazole, 4,5-dimethoxazole, S-phenyloxazole, benzoxazole, S-chlorobenzoxazole, S-methylbenzoxazole, 5-phenylbenzoxazole, 5- or fi-nitrobenzoxazole, S-chloro-G-nitrobenzoxazole, fi-methylbenzoxazole, 5,6- dimethylbenzoxazole, 4,6-dimethylbenzoxazole, 5-mothoxybenzoxazole, S-ethoxybenzoxazole, '5-chlorobenzoxazole, 6-methoxybenzoxazole, 5-hydroxybenzoxazole, 6-hydroxybenzoxazole, naphth[2,1-d]oxazole, naphth- [1,2-d]oxazole, nitro group substituted naphthoxazoles, etc.;

a selenazole, nucleus, e.g., 4-rnethylselenazole, 4-nitroselenazole, 4-phenylselenazole, benzoselenazole, S-chlorobenzoselenazole, 5-methoxybenzoselenazole, 5-hydroxybenzoselenazole, 5- or G-nitrobenzoselenazole, 5- chloro 6 nitrobenzoselenazole, tetrahydrobenzoselenazole, naphtho[2, 1-d]selenazole, naphtho 1,2-d] selenazole, nitro group substituted naphthoselenazoles, etc.; thiazoline nucleus, e.g., thiazoline, 4-methylthiazoline, 4-nitrothiazoline, etc.;

a pyridine nucleus, e.g., 2-pyridine, 5-methyl-2-pyridine, 4-pyridine, 3-rnethyl-4-pyridine, nitro group substituted pyridines, etc.

a quinoline nucleus, e.g., 2-quinoline, 3-methyl-2-quinoline, 5-ethyl-2-quinoline, 6-chloro-2-quinoline, 6-nitro- 2-quinoline, 8-chloro-2-quinoline, o-methoxy-l-quino line, 8-ethoXy-2-quinoline, S-hydroxy 2 quinoline, 4- quinoline, 6 methoxy-4-quinoline, 6-nitro-4-quinoline, 7-methyl-4-quinoline, 8-chloro-4-quinoline, l-isoquinoline, G-nitro-I-isoquinoline, 3,4-dihydro-1-isoquinoline, 3-isoquinoline, etc.;

a 3,3-dial-kylindolenine nucleus, preferably having a nitro or cyano substituent, e.g., 3,3-dimethyl-5 or 6-nitroindolenine, 3,3-dimethyl-5- or 6-cyanoindolenine, etc.; and

an imidazole nucleus e.g., imidazole, l-alkylimidazole, 1alkyl-4-pheny1imidazole, l-alkyl-4,S-dimethylimidazole, benzimidazole, l-alkylbenzimidazole, 1-aryl-5,6- dichlorobenzimidazole, 1-alkyl-1H-naphthimidazole, 1- aryl-3H-naphth[ 1,2-d] imidazole, I-aIkyI-S- th 1H-naphth[ 1,2-d] imidazole, or

an imidazo[4,5-b]quinoxaline nucleus, e.g., 1,3 dialkylimidazo[4,5-b-]quinoxaline such as 1,3-diethylirnidazo- [4,5-b1quinoxaline, 6-chloro-1,3-diethylimidazo[4,5-b] quinoxaline, etc., 1,3-dialkylenylimidazo[4,5-b]quinwtaline sashe lQ-QiQ y uQiQ HJ- Jq wsl se chloro-l,3-dia1lylimidazo[4,5 b]quinoxaline, etc., 1,3- diarylimidazo[4,5-b] quinoxaline such as 1,3-diphenylimidazo[4,5-b] quinoxaline, 6-chloro 1,3 diphenylirnidazo [4,5 -b] quinoxaline, etc.;

a 1,3,3-trialkyl-3H-pyrrolo[2,3-b]pyridine nucleus, e.g.,

1,3,3-trimethyl-3H-pyrrolo[2,3-b] pyridine, 1,3,3-triethyl-3H-pyrrolo[2, 3-b] pyridine, etc.;

a thiazolo[4,5-b]quinoline nucleus; and the like.

Nuclei wherein Z represents an imidazo[4,5-b]quinoxaline nucleus, a 1,3,3-trialkyl-3H-pmolo[2,3-b1pyridine nucleus, a thiazolo [4,5-b1quinoline nucleus, a nitro group substituted thiazole, oxazole, selenazole, thiazoline, pyridine, quinoline, 1,3,3-tn'alkylindolenine, or imidazole nucleus are desensitizing nuclei.

The dyes defined above are powerful electron acceptors and spectral sensitizers for direct positive photographic silver halide emulsions. In addition, they are also useful desensitizers in emulsions used in the process described in Stewart and Reeves, US. Pat. No. 3,250,618, issued May 10, 1966.

As used herein desensitizing nucleus refers to those nuclei which, when converted to a symmetrical carbocyanine dye and added to gelatin silver chlorobromide emulsion containing 40 mole percent chloride and 60 mole percent bromide, at a concentration of from 0.01 to 0.2 gram dye per mole of silver, cause 'by electron trapping at least an percent loss in the blue speed of the emulsion when sensitometrically exposed and developed three minutes in Kodak developer D-19 at room temperature. Advantageously, the desensitizing nuclei are those which, when converted to a symmetrical carbocyanine dye and tested as just described, essentially complete desensitize the test emulsion to blue radiation (i.e., cause more than about to loss of speed to blue radiation).

Another highly useful class of novel cyanine dyes of the invention include those represented by the following general formula:

wherein R R R R R and X are as previously defined, R represents an alkyl group (preferably a lower alkyl containing from 1 to 4 carbon atoms), e.g., methyl, ethyl, propyl, isopropyl, butyl, hexyl, cyclohexyl, decyl, dodecyl, etc., or an aryl gruop, e.g., phenyl, tolyl, naphthyl, chlorophenyl, nitrophenyl, methoxyphenyl, etc., or a heterocyclic radical containing from 5 to 6 atoms in the heterocyclic ring and having a hetero nitrogen, oxygen or sulfur atom, preferably a heterocyclic radical selected from pyridyl (e.g., 2-, 3- or 4-pyridyl), 3-indolyl, or 2. thienyl; R represents a hydrogen atom or an aryl group, e.g., phenyl, tolyl, naphthyl, chlorophenyl, nitrophenyl, methoxyphenyl, etc.; and, D represents the non-metallic atoms necessary to complete a Z-arylindole nucleus (e.g., a l-alkyl (or aryl)-2-phenylindole, a 1- alkyl (or aryl)-5-nitro-2-phenylindole, etc) a pyrrolo- [2,3-bjquinoxaline nucleus (e.g., 1-butyl-7-chloropyrrolo- [2,3-b1quinoxaline, l-methyl-Z-p-tolylpyrrolo[2,3-b]quinoxaline, etc.) or a pyrrolo[2,3-b]pyrazine nucleus (e.g., 1-methylpyrrolo[2,3-'b pyrazine, etc.)

b lTypical representative dyes of this invention are listed e ow:

1,3'-diethyl- '-nitro-3-pyrrolo [2,3-b] quinoxalinothiacarbocyanine p-toluenesulfonate 1,3-diallyl- 1 -ethylimidazo [4, S-b] quinoxalino- -pyrrolo [2,3-b] quinoxalinocarbocyanine p-toluenesulfonate 1'-ethyl-1,3,3-trimethyl-3H-pyrrolo[2,3-b1pyrido-3 -pyr- .rolo ,3-b1q no eliuose bocya ins iodide 6-chloro-11'-ethy1-1,3-diphenylimidazo[4,5-b] quinoxalino- 3'-pyrrolo[2,3-b] quinoxalinocarbocyanine p-toluenesulfonate 1'-ethyl-l,3 ,3-trimethyl--nitroindo-3 '-pyrrolo [2,3-b]

quinoxalinocarbocyanine p-toluenesulfonate 1-butyl-7-chloro-3-ethyl- '-nitro-3-pyrro1o [2,3-b]

quinoxalinothiacarbocyanine p-toluenesulfonate 1,3-diallyl- 1 -butyl-7'-chloroimidazo [4,5 -b] quinoxalino- 3 '-pyrrolo [2,3-b] quinoxalinocarbocyanine bromide '-butyl-7-chloro- 1,3 ,3-trimethyl-5-nitroindo-3 '-pyrrolo[2,3-b] quinoxalinocarbocyanine bromide 3'-ethyl-1-methyl-6'-nitro-2-p-toly1-3-pyrrolo [2,3-b]

quinoxalinothiacarbocyanine p-toluenesulfonate 1,3-diallyl-1'-methyl- -p-tolylimidazo [4,5 -b] quinoxalino- -pyrrolo[2,3-b-] quinoxalinocarbocyanine p-toluenesulfonate 6-chloro- '-methyl-1,3-diphenyl-2'-p-tolylimidazo- [4,5-b] quinoxalino-3'-pyrrolo[2,3-b] quinoxalinocarbocyanine p-toluenesu1fonate 1,1',3,3-tetramethyl-5-nitro-2-to1ylindo-3 '-pyrrolo- [2,3-b] quinoxalinocarbocyanine p-toluenesulfonate 1,1,3,3-tetramethyl-2'-p-tolylpyrrolo[2,3-b]pyrido-3 pyrrolo [2,3-b] quinoxalinocarbocyanine perchlorate 1'-ethyl-1,3,3,8-tetramethyl-5-nitroindo-3'-pyrrolo- [2,3-b] quinoxalinocarbocyanine p-toluenesulfonate 1,1'-diethyl-11-phenyl-3-pyrrolo[2,3-b]quinoxalino-4'- carbocyanine bromide '-chloro-3 -ethyl-6-nitro-1'-phenyl- 8- 2-thienyl oxa- 3'-pyrrolo [2,3-b] quinoxalinocarbocyanine bromide 3-ethyl-1-methyl-6'-nitro-2-p-tolyl-3-pyrrolo[2,3-b]

quinoxalinoselenacarbocyanine bromide l,3' diethyl-S'-nitro-3-pyrrolo [2,3-b] quinoxalinothiazolinocarbocyanine p-toluenesulfonate 3-ethyll '-propyl-3 '-pyrrolo [2, 3 -b] quinoxalino-Z-thiazo1o[4,5-b] quinolinocarbocyanine bromide 5,6-diethyl-3',8'-dimethy1 5'-nitro-1-phenyl-3-pyrrolo- [2,3-b] pyrazinoselenacarb ocyanine bromide 1,3-dial1yl-1,1'-butyl-2'-phenylimidazo[4,5-b]quinolino- 3 '-pyrrolo [2,3-b] pyrazinocarbocyanine iodide 3 '-ethyl-5,6-dimethyl-5'-nitro-1-pheny1-3-pyrrolo- [2,3-b] pyrazinothiazolinocarb ocyanine iodide 3'-ethyl-9-methyl-1,5,6-triphenyl-3-pyrrolo [2,3-b]pyrazino-2'-thiazolo[4,5-b] quinolinocarbocyanine iodide 1,1'-dimethyl-2-(2-naphthyl)-2-phenyl-8-(2-thienyl)- 3-indolo3 '-pyrrolo [2,3 -b] quinoxalinocarbocyanine bromide 5,6-dimethyl-l, l'-diphenyl-8- 3-pyridyl)-3-pyrrolo- [2,3 -b] pyrazino-3'-pyrrolo [2,3 -b] quinoxalinocarbocyanine bromide 8- (2-furyl) -1-methyl-1 ,2-diphenyl-3 ,3 '-pyrrolo[2,3-b]

quinoxalinocarbocyanine perchlorate 8-ethyl-1'methyl-5, 6-diphenyl-3-pyrrolo [2, 3 -b] pyrazino-3 '-pyrrolo[2,3-b] quinoxalinocarbocyanine bromide 2-ethyl-1,l'-dimethyl-8-(2-naphthyl)-3,3'-pyrrolo- [2,3-b] pyrazinocarbocyanine bromide 1, l -dimethyl-2,8-diphenyl-2'-p-tolyl-S-indolo-3 '-pyrrolo- [2,3-b] quinoxalinocarbocyanine perchlorate 3 '-ethyl-6'-nitro-1-phenyl-3-py1rolo [2,3-b]pyrazinothiacarbocyanine p-toluenesulfonate 3-methyl-5-nitro-1'-phenyloxa- '-pyrrolo [2,3-b] pyrazinocarbocyanine p-toluenesulfonate 1,3-dimethyl- '-phenylimidazo[4,5-b]quinolino-3'-pyrrolo [2,3-b'] pyrazinocarbocyanine ptoluenesulfonate 6-chloro-l,1,3-triphenylimidazo[4,5-b]quinoxalino-3 pyrrolo [2,3-b] pyrazinocarbocyanine bromide 1',3',3-trimethyl l-phenyl-3 -pyrrolo[2,3-b] pyrazino- 3 H-pyrrolo [2, 3-b] pyridocarbocyanine p-toluenesulfonate 1,3,3-trimethyl-5-nitro-l'-phenylindo-3 '-pyrrolo[2,3-b]

pyrazinocarbocyanine p-toluenesulfonate These dyes also function as powerful electron acceptors and spectral sensitizers for direct positive photographic silver halide emulsions, as well as being useful sensitizers in emulsions used in the aforementioned process described in Steward and Reeves U.S. Pat. No. 3,250,618, issued May 10, 1966.

The cyanine dyes defined by Formula I above are conveniently prepared, for example, by heating a mixture of (l) a heterocyclic compound of the formula:

wherein n, R X and Z are as previously defined, and R represents methyl, ethyl, benzyl, etc., and (2) a heterocyclic compound of the formula:

V. R3 R4 wherein R R R and R are as previously defined, in approximately equimolar proportions, in a solvent medium such as acetic anhydride. The crude dyes are separated from the reaction mixtures and purified by one or more recrystallizations from appropriate solvents such as methanol alone or acidified with an acid such as p-toluenesulfonic acid, perchloric acid, etc.

The intermediates defined by Formula IV above may be prepared by means of the Vilsmeier reaction. For example by reacting (1) a compound of the formula:

V. j Nj om or a compound of the formula:

VI. N

N III R2 wherein R R R R and X are as previously defined, with (2) a complex of phosphoryl chloride, phosgene, oxalyl chloride, etc. and dimethyl formamide in excess dimethylformamide, as solvent, in approximate proportions of 1 mole of 1) to 3 or more moles of (2). The reaction mixtures are cooled, diluted with ice-Water mixture, and then made alkaline by addition of aqueous alkali metal hydroxide solution such as aqueous sodium hydroxide. The product is then separated by conventional methods, for example, by extraction of the mixture with a water-insoluble solvent such as chloroform, the residue being purified, if desired, by one or more recrystallizations from appropriate solvents such as dimethyl formamide.

The cyanine dyes defined by Formula II above are conveniently prepared, for example, by heating a mixture of 1) a compound of Formula IV above and (2) a compound of the formula:

x wherein D, R R and R are as previously defined, in approximately equimolar proportions, in a solvent medium, such as acetic anhydride, containing a strong mineral acid such as perchloric acid. After cooling and diluting with ether, the solid which separates is recrystallized. The preparation of intermediates corresponding to above Formula VH can be carried out by the general method described in M. Coenen et al., US. Pat. No. 2,930,694, issued Mar. 29, 1960.

In accordance with the invention, novel and improved direct positive photographic silver halide emulsions are prepared by incorporating one or more of the cyanine dyes of the invention into a suitable fogged silver halide emulsion. The emulsion can be fogged in any suitable manner, such as by light or with chemical fogging agents, e.g., stannous chloride, formaldehyde, thiourea dioxide, and the like. The emulsion may be fogged by the addition thereto of a reducing agent, such as thiourea dioxide, and a compound of a metal more electropositive than silver, such as a gold salt, for example, potassium chloroaurate, as described in British Pat. 723,019 (1955).

Typical reducing agents that are useful in providing such emulsions include stannous salts, e.g., stannous chloride hydrazine, sulfur compounds such as thiourea dioxide, phosphonium salts such as tetra(hydroxymethyl) phosphonium chloride, and the like. Typical useful metal compounds that are more electropositive than silver include gold, rhodium, platinum, palladium, iridium, etc., preferably in the form of soluble salts thereof, e.g., potassium chloroaurate, auric chloride, (NHQ PdCI and the like.

Useful concentrations of reducing agent and metal compound (e.g., metal salt) can be varied over a considerable range. As a general guideline, good results are obtained using about .05 to 40 mg. reducing agent per mole of silver halide and 0.5 to 15.0 mg. metal compound per mole of silver halide. Best results are obtained at lower concentration levels of both reducing agent and metal compound.

The concentration of added dye can vary widely, e.g., from about 50 to 2000 mg. and preferably from about 400 to 800 mg. per mole of silver halide in the direct positive emulsions.

As used herein, and in the appended claims, fogged refers to emulsions containing silver halide grains which produce a density of at least 0.5 when developed, without exposure, for minutes at 68 F. in developer Kodak DK-SO having the composition set forth below, when the emulsion is coated at a silver coverage of 50 mg. to 500 mg. per square foot.

Water to make 1.0 l.

The dyes of this invention are also advantageously incorporated in direct positive emulsions of the type in which a silver halide grain has a water-insoluble silver salt center and an outer shell composed of a fogged waterinsoluble silver salt that develops to silver without exposure. The dyes of the invention are incorporated,

preferably, in the outer shell of such emulsions. 'Ihese emulsions can be prepared in various ways, such as those described in Berriman' US. patent application Ser. No. 448,467, filed Apr. 15, 1965. For example, the shell of the grains in such emulsions may be prepared by precipitating over the core grains a light-sensitive water-insoluble silver salt that can be fogged and which fog is removable by bleaching. The shell is of sufficient thickness to prevent access of the developer used in processing the emulsions of the invention to the core. The silver salt shell is surface fogged to make it developable to metallic silver with conventional surface image developing compositions. The silver salt of the shell is suflieiently fogged to produce a density of at least about 0.5 when developed for 6 minutes at 68 F. in Developer A below when the emulsion is coated at a silver coverage of 100 mg. per square foot, Such togging can be eifected by chemically sensitizing to fog with the sensitizing agents described for chemically sensitizing the core emulsion, high intensity light and the like fogging means Well known to those skilled in the art. While the core need not be sensitized to fog, the shell is fogged. Foggin-g by means of a reduction sensitizer, a noble metal salt such as gold salt plus a reduction sensitizer, a sulfur sensitizer, high pH and low pAg silver halide precipitating conditions, and the like can be suitably utilized. The shell the silver salt core, the core emulsion is first chemically or physically treated by methods previously described in the prior art to produce centers which promote the deposition of photolytic silver, i.e., latent image nucleating centers. Such centers can be obtained by various techniques as described herein. Chemical sensitization techniques of the type described by Antoine Hautot and Henri Sauvenier in Science et Industries Photographiques, Vol. XXVIII, January 1957, pages 1 to 23 and January 1957, pages 57 to 65 are particularly useful. Such chemical sensitization includes three major classes, namely, gold or noble metal sensitization, sulfur sensitization, such as by a labile sulfur compound, and reduction sensitization, e.g., treatment of the silver halide with a strong reducing agent which introduces small specks of metallic silver into the silver salt crystal or grain.

The dyes of this invention are highly useful electron acceptors in high speed direct positive emulsions comprising fogged silver halide grains and a compound which accepts electrons, as described and claimed in Illingsworth US. patent application Ser. No. 609,794, filed Jan. 17, 1967, and titled Photographic Reversal Materials 111, Th'e fogged silver halide grains of such emulsions are such that a test portion thereof, when coated as a photographic silver halide emulsion on a support to give a maximum density of at least about one upon processing for six minutes at about 68 F. in Kodak DK-50 developer, has a maximum density which is at least about 30% greater than the maximum density of an identical coated test portion which is processed for six minutes at about 68 F. in Kodak DK-50 developer after being bleached for about 10 minutes at about 68 F. in a bleach composition of:

Water to 1 liter.

The grains of such emulsions will lose at least about 25% and generally at least about 40% of their fog when bleached for ten minutes at 68 F. in a potassium cyanide bleach composition as described herein. This fog loss can be illustrated by coating the silver halide grains as a photographic silver halide emulsion on a support to give a maximum density of at least 1.0 upon processing for six minutes at about 68 F. in Kodak DK-SO developer and comparing the density of such a coating with an identical coating which is processed for six minutes at 68 F. in Kodak D K-SO developer after being bleached for about 10 minutes at 68 F. in the potassium cyanide bleach composition. As already indicated, the maximum density of the unbleached coating will be at least 30% greater, generally at least 60% greater, than the maximum density of the bleached coating.

The silver halides employed in the preparation of the photographic emulsions useful herein include any of the photographic silver halides as exemplified by silver bromide, silver iodide, silver chloride, silver chlorobromide, silver bromoiodide, silver chlorobromide, and the like. Silver halide grains having an average grain size less than about one micron, preferably less than about 0.5 micron, give particularly good results. The silver halide grains can be regular and can be any suitable shape such as cubic or octahedral, as described and claimed in lllingsworth US. patent application Ser. No. 609,778, filed Jan. 17, 1967, and titled Direct Positive Photographic Emulsions 1. Such grains advantageously have a rather uniform diameter frequency distribution, as described and claimed in lllingsworth U.S. patent application Ser. No. 609,790, filed Ian. 17, 1967, and titled Photographic Reversal Emulsions 11. For example, at least 95%, by weight, of the photographic silver halide grains can have a diameter which is within about 40%, preferably within about 30% of the mean grain diameter. Mean grain diameter, i.e., average grain size, can be determined using conventional methods, e.g., as shown in an article by Trivelli and Smith entitled Empirical Relations Between Sensitometn'c and Size-Frequency Characteristics in Photographic Emulsion Series in The Photographic Journal, vol. LXXJX, 1949, pages 330-338.. The fogged silver halide grains in these direct-positive photographic emulsions of this invention produce a density of at least 0.5 when developed without exposure for five minutes at 68 F. in Kodak DK-50 developer when such an emulsion is coated at a coverage of 50 to about 500 mg. of silver per square foot of support. The preferred photographic silver halide emulsions comprise at least 50 mole percent bromide, the most preferred emulsions being silver bromoiodide emulsions, particularly those containing less than about ten mole percent iodide. The photographic silver halides can be coated at silver coverages in the range of about 50 to about 500 milligrams of silver per square foot of support.

In the preparation of the above photographic emulsions, the dyes of the invention are advantageously incorporated in the washed, finished silver halide emulsion and should, of course, be uniformly distributed throughout the emulsion. The methods of incorporating dyes and other addenda in emulsions are relatively simple and well known to those skilled in the art of emulsion making. For example, it is convenient to add them from solutions in appropriate solvents, in which case the solvent selected should be completely free from any deleterious effect on the ultimate light-sensitive materials. Methanol, isopropanol, pyridine, water, etc., alone or in admixtures, have proven satisfactory as solvents for this purpose. The type of silver halide emulsions that can be sensitized with the new dyes include any of those prepared with hydrophilic colloids that are known to be satisfactory for dispersing silver halides, for example, emulsions comprising natural materials such as gelatin, albumin, agar-agar, gum arabic, alginic acid, etc. and hydrophilic synthetic resins such as polyvinyl alcohol, polyvinyl pyrrolidone, cellulose ether-s, partially hydrolyzed cellulose acetate, and the like The binding agents for the emulsion layer of the photographic element can also contain dispersed polymerized vinyl compounds. Such compounds are disclosed, for example, in US. Pats. 3,142,568; 3,193,386; 3,062,674 and 3,220,844 and include the water insoluble polymers of alkyl acrylates and methacrylates, acrylic acid, sulfoalkyl acrylates or methacrylates and the like.

The dyes, reducing agents and metal compounds of the invention can be used with emulsions prepared, as indicated above, with any of the light-sensitive silver halide salts including silver chloride, silver bromide, silver chlorobromide, silver bromoiodide, silver chlorobromoiodide, etc. Particularly useful are direct positive fogged emulsions in which the silver salt is a silver bromohalide comexamples.

EXAMPLE 1 1,3 '-diethyl-6'-nitro-3 -pyrrolo [2,3-b] quinoxalinothiacarbocyanine p-toluenesulfonate 1 ethyl 3 formylpyrrolo[2,3-b]quinoxaline (0.56 g., 1 mol.) and 3-ethyl-2-methyl-6-nitrobenzothiazolium ptoluenesulfonate (0.99 g., 1 mol.) in acetic anhydride (10 ml.) are heated at reflux for 1 minute. The cooled solution is slowly diluted with excess ether and the solid which is precipitated is collected and washed with ether. After one recrystallization from methanol, the yield of purified dye is 0.77 g. (51%), M.P. 28l282 C., dec.

The above prepared dye containing the desensitizing 3- ethyl-6-nitrobenzothiazole nucleus is photographically tested for its usefulness as an electron acceptor and spectral sensitizer for fogged direct positive photographic silver halide emulsions by the following procedure.

A gelatin silver bromoiodide emulsion (2.5) mole per cent of the halide being iodide) and having an average grain size of about 0.2 micron is prepared by adding an aqueous solution of potassium bromide and potassium iodide, and an aqueous solution of silver nitrate, simultaneously to a rapidly agitated aqueous gelatin solution at a temperature of 70 C., over a period of about 35 minutes. The emulsion is chill-set, shredded and washed by leaching with cold water in the conventional manner. The emulsion is reduction-gold fogged by first adding 0.2 mg. of thiourea dioxide per mole of silver and heating for 60 minutes at 65 C. and then adding 4.0 mg. of potassium chloroaurate per mole of silver and heating for 60 minutes at 65 C. The dye of the above example, 1,3 diethyl 6 nitro-3-pyrrolo[2,3-b]quinoxalinothiacarbocyanine p-toluenesulfonate, is then added to the above fogged emulsion in amount sufiicient to give a concentration of 0.08 gram of the dye per mole of silver. The resulting emulsion is coated on a cellulose acetate film support at a coverage of mg. of silver and 400 mg. of gelatin per square foot of support.

A sample of the coated support is then exposed on an Eastman Ib sensitometer using a tungsten light source and processed for 6 minutes at room temperature in Kodak D-l9 developer which has the following composition:

Water to make 1.0 liter.

then fixed, washed and dried. The results are listed in Table I hereinafter. Referring thereto, it will be seen that the dye of this example has a maximum density in the unexposed areas of 1.63 and a minimum density in exposed areas of 0.06, a maximum sensitivity of 550 nm. and a relative speed of 380. This result indicates that the dye compound of the above example is well suited to function as both an electron acceptor and spectral sensitizer. It thus provides excellent quality direct positive photographic silver halide emulsions. Excellent magenta images are obtained when the color former 1- (2,4,6-trichlorophenyl) 3 {3-[(2,4-di-tert-pentylphenoxy) acetamido}-benzamido}-2-pyrazolin-S-one is incorporated in the emulsion of this example, the emulsion is coated on a support, exposed to a tungsten source through Wratten filter No. 61 and No. 1 6, and reversal processed as described in Graham et al. U.S. Pat. 3,046,129, issued July 24, 1962, in Example (a) C01. 27, lines 27 et seq. except that black-and-white (MQ) development is omitted, the color development is reduced to one minute and is conducted in total darkness until after fixing.

In place of the 3-ethyl-2-methyl-6-nitrobenzothiazolium p-toluenesulfonate in the above example, there can be substituted an equivalent amount of any other of the intermediates defined by Formula III above to give the corresponding other cyanine dyes of the invention having generally similar properties as electron acceptors and spectral sensitizers for photographic silver halide emulsions, and more particularly for direct positive photographic emulsions, for example, the dye l',3-diethyl-6- nitrooxa 3'-pyrrolo[2,3-b]quinoxalinocarbocyanine salt (e.g., the chloride, bromide, iodide, perchlorate, p-toluenesnlfonate, etc. salt); the dye 1,3-diethyl- '-nitro-3-pyrro1o- [2,3-b]quinoxalinoselenacarbocyanine salt (e.g., the chloride, bromide, iodide, perchlorate, p-toluenesulfonate, etc. salts); and the like cyaniue dyes.

EXAMPLE 2 CHz-CH=CH2 This compound is prepared and isolated by the same procedure as that described for Example 1, except that 1,3 diallyl-2-methylimidazo[4,5-b] quinoxalinium p-toluenesulfonate (1.09 g., 1 mol.) is used instead of 3-ethyl- 2 methyl 6 nitrobenzothiazolium p-tolnenesulfonate. After two recrystallizations from methanol, the yield of purified dye is 0.28 g. (17%), M.P. 250-252 Cd. dec.

The above prepared dye containing the desensitizing 1,3 diallylimidazo[4,5-b]quinoxaline nucleus is photographically tested by the procedure described in above Example 1. The results are recorded in Table 1 hereinafter. Reference thereto indicates that this dye is an excellent electron acceptor and spectral sensitize! for fogged direct positive photographic emulsions. The densities are 1.30 and 0.02 for the unexposed and exposed areas, respectively, with a maximum sensitivity at 538 um. and a relative speed of .912.

1 2 EXAMPLE 3 1'-ethyl-1,3,3-t1imethyl-3H-pyrrolo[2,3-b]pyrido-3- pyrrolo[2,3-b] quinoxalinocarbocyanine iodide 1 ethyl 3-formylpyrrolo[2,3-b] quinoxaline (0.56- g., 1 mol.), 1,3,3-trimethyl-2-methylene-2,3-dihydropyrrolo- [2,3-b1pyridine (0.44 'g., 1 mol.) and p-toluenesulfonic acid monohydrate (0.48 g., 1 mol.) in acetic anhydride (10 ml.) are heated at reflux for 1 minute. When cool, the mixture is diluted with excess ether and the product separated as an oil. The oil is dissolved in boiling methanol ml.) containing 47% aqueous HI (1.25 ml.). The solution is filtered, then chilled. The solid which crystallizes is collected and after a further recrystallization from methanol, the yield of purified dye is 0.38 g. (26% M.P. indistinct.

This dye containing the desensitizing 1,3,3-trirnethyl- 3H-pyrrolo[2,3-b]pyridine nucleus is tested in accordance with the test procedure of Example 1. The results of the test are recorded in Table 1 hereinafter. The densities are 1.65, and 0.03 for the unexposed and exposed areas, respectively, with maximum sensitivity at 5 30 nm. and a relative speed of 708. Accordingly, this dye is an excellent electron acceptor and spectral sensitizer for fogged direct positive photographic emulsions.

EXAMPLE 4 6-chlorol'-ethyl 1,3 diphenylimidazo[4,5-b]quinoxalino 3' pyrrolo[2,3-b]quinoxalinocarbocyanine ptoluenesulfonate N\ /N j /N can-German osomm This dye is prepare and purified in the same manner as that described for Example 2, except that '6-chloro-2- methyl-1,3 diphenylimidazo[4,5-b] quinoxalinium p-toluenesulfonate (1.36 g., 1 mol.) is used in place of 1,3- diallyl-Z-methylimidazo[4,5-b]quinoxalinium p toluenesulfonate. The yield of purified dye is 0.21 g. (11%), M.P. 300 C.

The above prepared dye containing the desensitizing l,3-diphenylimidazo[4,5-b]quinoxaline nucleus is tested by the procedure described in above Example 1. Reference thereto indicates that this dye is an outstanding electron acceptor and spectral sensitizer for fogged direct positive photographic emulsions. The densities are 1.64 and 0.02 for the unexposed and exposed areas, respectively, with maximum sensitivity at 550 nm. and a relative speed of 891.

EXAMPLE 5 1'-ethyl-l,3,3-trimethyl-5-nitroindo-3'-pyrrolo[2,3-b]

qulnoxalinocarbocyanine p-toluenesulfona This dye is prepared and purified in the same manner as that described for Example 2, except that 1,2,3,3-tetramethyl--nitro-3H-indolium p-toluenesulfonate (0.98 g., 1 mol.) is used in place of 1,3-diallyl-2-methylimidazo- [4,5-b]quinoxalinium p-toluenesulfonate. The yield of purified dye is 0.56 g. (38%), M.P. 257-258 C., dec.

This dye containing the desensitizing 1,3,3-trimethyl- 5-nitro-3H-indole nucleus is tested in accordance with the test procedure of above Example 1. The results are recorded in Table 1 hereinafter. Referring to the table, it will be seen that the densities are 1.64 and 0.10 for the unexposed and exposed areas, respectively, with maximum sensitivity at 550 nm. and a relative speed of 661. This dye is accordingly, an excellent electron acceptor and spectral sensitizer for fogged direct positive photographic emulsions.

EXAMPLE 6 l-butyl-7-chloro-3'-ethyl- -nitro-3-pyrrolo[2,3-b]quinoxalinothiacarbocyanine p-toluenesulfonate if \N This dye is prepared in the same manner as Example 1, except that 1-butyl-7-chloro-3-formylpyrrolo[2,3-b]quinoxaline (0.72 g., 1 mol.) is used in place of 1-ethyl-3- formylpyrrolo[2,3-b]quinoxaline. After two recrystallizations from methanol, the yield of purified dye is 0.85 g. (51%), MP. 248-9 C., dec.

The above prepared dye containing the desensitizing 1-ethyl-6-nitrobenzothiazole nucleus is an excellent electron acceptor and spectral sensitizer for fogged photographic reversal emulsions as indicated by the test procedure of above Example 1, the results of which are recorded in Table 1 hereinafter. The densities are 1.82 and 0.05 for the unexposed and exposed areas, respectively, with a maximum sensitivity at 535 nm., and a relative speed of 692.

EXAMPLE 7 1,3-diallyl-1'-'butyl-7 '-chloroimidazo [4, 5 -b] quinoxaline- 3 -pyrrolo [2, 3-b] quinoxalinocarb ocyanine bromide hnon=orn e The dye is prepared in the same manner as Example 2, except that 1-butyl-7-chloro-3-formylpyrrolo[2,3-b]quinoxaline (1.09 g., 1 mol.) is used in place of 1-ethyl-3- formylpyrrolo[2,3-b]quinoxaline. After two recrystallizations from methanol containing HBr, the yield of puritied dye is 0.72 g. (46%), M.P. 206-8 C., dec.

The above prepared dye containing the desensitizing 1,3-diallylirnidazo[4,5-b]quinoxaline nucleus is tested by the procedure of Example 1. The resultsare recorded in Table 1 hereinafter. Referring th'ereto, the densities are 1.90 and 0.03 for the unexposed and exposed areas, respectively, with maximum sensitivity at 530 nm. and a relative speed of 955. This dye is, accordingly, an excellent electron acceptor and spectral sensitizer for fogged direct positive photographic emulsions.

EXAMPLE 8 1 '-butyl-7 '-chloro- 1,3 3 -trimethyl-5-nitroindo-3 -pyrrolo[2,3-b]quinoxalinocarbocyanine bromide This dye is prepared in the same manner as Example 5, except that 1-butyl-7-chloro-3-formylpyrrolo[2,3-b] quinoxaline (0.72 g., 1 mol.) is used in place of l-ethyl- 3-formylpyrrolo[2,3-b]quinoxaline. After two recrystallizations from methanol containing HBr, the yield of purified dye is 0.71 g. (53%), M.P. 248-50" C., dec.

This dye containing the desensitizing 1,3,3-trimethyl- 5-nitro-3H-indole nucleus is an excellent electron acceptor and spectral sensitizer for fogged direct positive photographic emulsions as indicated by the test procedure of above Example 1, the results of which are recorded in Table I hereinafter. The densities are 1.86 and 0.04 for the unexposed and exposed areas, respectively, with maximum sensitivity at 548 nm. and a relative speed of 661.

The following Examples 9 to 14 illustrate the preparation of cyanine dyes of the invention wherein R of Formula I above is an aryl substituent. The results obtained with these dyes by the testing procedure of above Example 1 are listed in Table 1 hereinafter.

EXAMPLE 9 3 '-ethyl-1-methyl-6'-nitro-2-p-tolyl3 -pyrrol0 [2,3b] quinoxalinothiacarbocyanine p-toluenesulfonate Hz-N s j N02 0 somm EXAMPLE 10 1,3-diallyl-1'-methyl 2' p tolylimidazo[4,5-b]quinoxaliuo-3' pyrrolo[2,3-b]quinoxalinocarbocyanine p-toluenesulfonate This dye is prepared and purified in the same manner as that described in Example 9, except that 1,3-diallyl-2- methylimidazo[4,5 bJquinoxalinium p-toluenesulfonate (1.09 g., 1 mol.) is used in place of 3-ethyl-2-methyl-6- nitrobenzothiazolium p-tolueuesulfonate. The yield of purified dye is 1.28 g. (71%), M.P. 269 C., (dec.).

EXAMPLE ll 6-chloro-1'-rnethyl 1,3-diphenyl-2'-ptolylimidazo[4,5-b]

quinoxaline 3' pyrrolo[2,3-b]quinoxalinocarbocyanine p-toluenesulfonate This dye is prepared and purified in the same manner as that described in Example 9, except that 6-chlloro-L3- diphenylimidazo [4,5 -b] quinoxaliniurn p-toluenesulfonate (1.36 g., 1 mol.) is used in place of 3-ethy1-2-rnethyl-6- nitrobenzothiazoliurn p-toluenesulfonate. The yield of purified dye is 0.69 g. (33%), M.P. 300 C.

EXAMPLE 12 1, l ,3 3 -tetrame-thyl--nitr0-2'-p-tolylindo-3 -pyrrolo- [2,3-b]quinoxalinocarbocyanine p-toluenesulfonate This dye is prepared and purified in the same manner as that described in Example 9, except that 1,2,3,3-tetramethyl-S-nitro-3I-I-indolium p-toluenesulfonate (0.98 g., 1 mol.) is used in place of 3-ethyl-Z-methyl-fi-nitrobenzo thiazolium p-toluenesulfonate. The yield of purified dye is 0.78 g. (46%)), M.P. 186-8 C., (dec.).

EXAMPLE 13 1, 1,3 .3-tetramethyl-2'-p-tolylpyrrolo 2,3-b] pyrido) -3 pyrrolo[2,3-b]quinoxalinocarbocyanine perchlorate CH3 CH3 N CHz-N on=on N N on Q a 010,

This dye is prepared in the same manner as that described in Example 9, except that l,2,3,3-tetrarnethyl-3H- pyrrolo[2,3-b]pyridinium p-toluenesulfonate (0.89 g., 1 mol.) is used in place of 3-ethyl-2-methyl-6-1Jitrobenzothiasol um po ue esulfoaate- Th yie d of p fi d y 16 is 0.88 g. (63%), M.P. 295 C. (dec.) after recrystallization from methanol containing perchloric acid.

EXAMPLE 14 1,1-dimethy1-2,8-cliphenyl-2-p-tolyl-3-indolo-3'-pyrrolo[2,3-b]quinoxalinocarbocyanine perchlorate 3-formyl-1-methyl 2-p-tolylpyrrolo [2,3-b1quinoxaline (0.75 g., 1 mol.) and 1-methyl-3-methylenebenzyl-2- phenylindole (0.77 g., 1 mol.) are added to a solution of 72% perchloric acid (0.28 g.) in acetic anhydride (10 1111.). The mixture is heated on a steam bath for 15 minutes, as green crystals separate. The mixture is allowed to cool, diluted with a little ether, and the solid collected. After recrystallization from acetic acid, the yield of purified dye is 1.04 g. (60%) M.P. 225 C. (dec.).

In place of the 1-methyl-3-methylenebenzyl-2-pheny1- indole in the above Example 14, there can be substituted an equivalent amount of, for example, 1-methyl-3-methylenebenzy12-p-tolylpyrrolo[2,3-b]quinoxaline to give the corresponding dye having generally similar properties as an electron acceptor and spectral sensitizer for direct positive photographic silver halide emulsions.

The following Examples 15 to 20* illustrate the preparation of cyanine dyes of the invention containing the l-aryl- 3-pyrrolo[2,3-b]pyrazine nucleus, i.e., wherein R and R of Formula I each represent hydrogen, alkyl, or aryl. The results obtained with these dyes by the testing procedure described in above Example 1 are recorded in Table 1 hereinafter.

EXAMPLE 15 3'-ethyl-6-nitro-1 phenyl-3-pyrrolo[2,3-b]pyrazinothiacarbocyanine p-toluenesulfonate pyrr0lo[2,3-b]pyrazine, 1.98 g. (1 mol.) of 3-ethyl-2- methyl-6-nitrobenzothiazolium p-toluenesulfonate, and 10 ml. of acetic anhydride are heated at reflux for 2 minutes. After chilling, the crude dye is collected on a filter and washed first with acetic anhydride, then with ether. After two recrystallizations from acetic acid, 2.47 g. (87%) of pure dye is obtained as shiny orange plates, M.P. 200- 202 C. (dec.).

EXAMPLE 16 3-rnethy1-5 -nitro-1 -pheny1oxa-3 '-pyrr0lo [2,3-h] pyrazinocarbocyanine p-toluenesulfonate A mixture of 1.12 g. (1 mol.) of 3-formyl-l-phenylpyrrolo[2,3-b]pyrazine, 1.82 g. (1 mol.) of 2,3-dimethylfi-nitrobe zo azqlium poluene sultonate and lo 0f 17 acetic anhydride are heated at reflux for 2 minutes. The solution is chilled and diluted with 50 ml. of ether. The crude dye is collected on a filter and washed with ether. After recrystallization from acetic acid, 1.16 g. (54%) of pure dye is obtained as bright yellow crystals, M.P. 232-235 C. (dec.).

EXAMPLE 17 1,3-dimethyl 1 phenylimidazo[4,5-b] quinoxalino-3- pyrrolo[2,3 b]pyrazinocarbocyanine p toluenesulfonate CH3 N N l, N m c.H. cn=cn N \N (in: osozoim 6-chloro-1,1',3-triphenylimidazo[4,5-b]quinoxalino-3 pyrrolo [2,3-b] pyrazinocarbocyanine bromide earn-N 011:011

/ \el -01 Br N N A mixture of 1.12 g. (1 mol.) of 3-formyl-1-phenylpyrrolo[2,3-b]pyrazine, 2.72 g. (1 mol.) of 6-chloro-2- methyl-1,3-diphenylimidazo[4,5-b]quinoxalinium p toluenesulfonate, and ml. of acetic anhydride is heated at reflux for 2 minutes. After chilling, the solution is diluted with 300 ml. of ether and the resultant solid, which proved to be very hydroscopic, is collected rapidly on a filter. The solid is dissolved in 200 ml. of warm methyl alcohol and treated with a solution of 1.0 g. (2 mols.) of sodium bromide in 10 ml. of water. The crude dye is collected on a filter and washed first with methyl alcohol, and then with water. After stirring in 100 ml. of hot methyl alcohol and filtering while hot, 0.93 g. (28%) of pure dye is obtained as a dull yellow powder, M.P. 300 C.

EXAMPLE 19 1',3,3'-trimethyl l-phenyl 3-pyrrolo[2,3-b]pyrazino-= 3H pyrrolo[2,3-b]pyridocarbocyanine p-toluenesulfonate A mixture of 1.12 g. (1 mol.) of 3-formyl-1-phenylpyrrolo[2,3-b]pyrazine, 0.87 g. (1 mol.) of 1,3,3-trimethyl-2-methylene-2,3-dihydropyrrolo[2,3 b]pyridine, 1.0 g. (1 mol.) of p-toluenesulfonic acid monohydrate and 10 ml. of acetic anhydride are heated at reflux for 2 minutes. After chilling, 350 ml. of ether are added, and the viscous oil is separated from the supernatant liquid by decantation. The oil is stirred with 100 ml. of ether which induced crystallization. The crude dye is collected on a 18 filter, and washed with ether. After recrystallization, first from methyl alcohol-toluene and then from dioxane, 0.26 g. (9%) of pure dye is obtained as brown crystals, M.P. 206-210 C. (dec.).

EXAMPLE 20 1,3,3-trimethyl-5-nitro-1'-phenylindo-3'-pyrrolo[2,3-b] pyrazino-carbocyanine p-toluenesulfonate A mixture of 1.12 g. (1 mol.) of 3-formyl-l-phenylpyrrolo[2,3-b]pyrazine, 1.95 g. (1 mol.) of 1,2,3,3-tetramethyl-5-nitro-3H-indolium p-toluenesulfonate, and 10 m1. of acetic anhydride is heated at reflux for 2 minutes. After chilling 20 ml. of ether are added. The crude dye is collected on a filter and washed with ether. Two recrystallizations from acetic acid yields 1.57 g. (53%) of pure dye as bright orange crystals, M.P. 255 C. (dec.).

The effectiveness of the dyes of the invention as electron acceptors and spectral sensitizers for fogged direct positive photographic silver halide emulsions, as determined by the exact testing procedure described in above Example 1, is recorded in the following table.

TABLE 1 Density Dye Relaconc., tive Max. Min.-

g. lmole clear unexposed exposed Sensitivity silver speed areas areas max. (11m.

None 1 1. 90 No reversal 50 380 1. 63 0. 06 550 912 1. 30 0.02 538 80 708 1. 65 0. 03 530 50 891 1. 64 0. 02 550 50 661 1. 64 O. 10 550 25 692 1. 82 0. 05 535 50 955 1. 0. 03 530 25 661 1. 86 0. 04. 548 35 1, 050 1.18 0. 04 550 35 1, 150 1. 38 0. 04 540 35 1, 910 1. 37 0. 04 575 35 1, 320 1. 24 0. 06 575 70 1, 620 1. 34 0. 04.- 545 35 1, 620 1.33 0.05 650 60 871 1. 60 0. 10 525 70 417 1. 46 0. 06 470 90 759 1. 68 0.31 530 35 457 1. 56 0. 19 521) 70 832 l. 52 0. 07 535 7 O 501 1. 38 0. 07 500 It will be noted from the above Table I that Examples 9 to 14, wherein R of Formula I above is an aryl substitnent, show very good reversals and outstanding relative speeds ranging from 1050 to 1620, with maximum sensitivity at from 540 to 650 nm. Examples 1 to 8 and 15 to 20 also show excellent reversal properties together with good speeds and desirable sensitivity maximums. In comparison with the above results, the control sample containing no dye shows a relative speed of less than 1 with no reversal indicated.

The following examples further illustrate the preparation of fogged, direct positive photographic emulsions and elements with the cyanine dyes of the invention.

EXAMPLE 21 To 9.0 pounds of a silver chloride gelatin emulsion containing an equivalent of grams of silver nitrate is added 0.017 gram of 6-chloro-1-ethyl-1,3-diphenylimidazo [4,5-b]quinoxalino 3 pyrrolo[2,3-b]quinoxa1inocarbocyanine p-toluenesulfonate (Example 4). The emulsion is coated on a non-glossy paper support, and is flashed with white light to give a density of 1.2 when developed 19 in the following developer, diluted 1 part to 2 parts of water:

Water to 1 liter.

The light fogged material can be exposed to an image with light modulated by a Wratten No. 15 filter to give a direct positive image. Generally similar results are obtained when the dyes of Examples 2, 10 and 15 are used in place of the above dye.

EXAMPLE 22 Seven pounds of a silver chloride gelatin emulsion containing the equivalent of 100 g. of silver nitrate is heated to 40 C. and the pH is adjusted to 7.8. Eight cc. of full strength (40%) formalin solution is added and the emulsion is held at 40 C. for 10 minutes. At the end of the holding period, the pH is adjusted to 6.0 and 0.125 g. of 1,3-diallyl-1'-butyl 7-chloroimidazo[4,5-b]quinoxalino- 3-pyrrolo [2,3-b] quinoxalinocarbocyanine bromide (Example 7). The emulsion is coated on a support, and provides good direct positive images. Similar results are obtained when the dyes of Examples '5, 6, 8 and 11 are substituted for the above dye.

The examples which follow illustrate the preparation of a number of intermediate l-alkylpyrrolo[2,3-b]quinoxalines employed in the preceding eyanine dye examples.

EXAMPLE A 2-ethylamino-Ii-mcthylquinoxaliue hydro-ptoluenesulfonate 2-chloro-3-methylquinoxaline (35.8 g., 1 mol.) [which may be prepared by the method of Platt and Sharp, J. Chem. Soc. (1948) 2132], anhydrous ethylamine (18.0 g., 1 mol.+l%) and ethanol (200 ml.) are heated at 160-175" C. in an autoclave for hours. The mixture is allowed to cool and the ethanol evaporated under reduced pressure. The product is dissolved in tetrahydrofuran (200 ml.) and the insoluble material filtered 01f, washed with a little tetrahydrofuran and rejected. The filtrate and washings are combined and cooled below 10 C. in an ice-bath as a solution of p-toluenesulfonic acid monohydrate (38.0 g., 1 mol.) in tetrahydrofuran is added slowly. The solid which precipitated is collected and washed with tetrahydrofuran. The yield of buff colored solid is 48.8 g. (68%), M.P. 193-195 C. This material is used without further purification.

EXAMPLE B 1-ethyl-3 -formylpyrrolo [2,3-b] quinoxaline C H O 2-ethylamino-3-methylquinoxaline hydro p-toluenesulfonate (7.18 g., 1 mol.) is suspended in dimethylformamide (25 ml.) and triethylamine (2.02 g., 1 mol.) is added. The resulting solution is added to a solution of phosphoryl chloride (9.25 g., 3 mols.) in dimethylformamide (11 ml.) at room temperature. Some heat is evolved. The mixture is heated on a steam-bath for 3 hours, then poured into water (200 ml.), 5 N NaOH (125 osomrr.

20 ml.) is added and the mixture stirred for 15 minutes. The product is extracted with chloroform, the extract dried over MgSO and the chloroform evaporated. The oily residue, which becomes partially crystalline on standing, is stirred With ligroin (50 ml.) and the solid collected and washed with ligroin. The yield of light grey solid is 1.6 g. (30%), M.P. 154155" C. This material is used without further purification.

EXAMPLE C 7-chloro3-methyl-2 1H) -quinoxalinone 4-clrloro-o-phenylenediamine (71.5 g., 1 mol.) is dissolved in a mixture of water (300 ml.) and cone. HCl ml.), then pyruvic acid (44.0 g., 1 mol.) is added, with stirring. After 11 2 hrs., the solid is collected and well washed with water. After recrystallization from dimethylformamide/ethanol, the yield is 47.4 g. (49%), M.P. 24850 C.

EXAMPLE D 2,7 -dichloro-3-methylquinoxaline N Q 10H; c1 01 7-clrloro-3-methyl 2(1H)-quinoxalinone (39.0 g., 1 mol.) and phosphoryl chloride (300 ml.) are heated at reflux for 10 min., to give a dark colored solution. The excess phosphoryl chloride is evaporated under reduced pressure, then excess ice added. Water is added to give a total volume of 750 ml., and the mixture is well stirred. The solid is collected and washed with water. After recrystallization from aqueous ethanol, the yield is 18.8 g. (44%), M.P. Ill-3 C.

EXAMPLE E 1 -butyl-7-chloro-3 -formylpyrrolo [2,3-b] quinoxaline CHO i C1 (CHz)aCHt 2,7-dichloro-3-methylquinoxaline (17.1 g., 1 mol.), butylamine (11.7 g., 1 m0l.+100%) and ethanol (40 ml.) are heated under reflux for 2 hrs. The ethanol is evaporated and the residue is diluted with ether. The solid is filtered 01f and rejected. Evaporation of the ether gives crude 2-butylamino-7-cl1loro 3 methylquinoxaline, to which is added a warm solution of phosphoryl chloride (37 g., 3 mol.) in dimethyl formamide (44 ml.). A vigorous reaction occurs. When the reaction subsides, the mixture is allowed to cool, then poured in 400 ml. of an ice/water mixture. 5 N NaOH (360 ml.) is added slowly, as more ice is added periodically to keep the mixture cool. The aqueous layer is decanted and the viscous residue digested with ethanol (50 ml.). After chilling, the solid is collected and washed with ethanol. After one recrystallization from dimethyl formamide, the yield is 4.56 g. (19%), M.P. 169-170 C.

EXAMPLE F 2-p-tolyl-1H-pyrrolo [2,3 -b] quinoxah'ne 4-methylimino-2-p-tolyl-2-pyrrolin-5-one hydrochloride (15.4 g., 1 mol.) [which may be prepared by the method of Mumm and 'Hornhardt. Ber. 70, 1930-47 (1937)], ophenylene diamine (7.0 g., 1 mol.) and acetic acid (65 ml.) are placed in a flask and heated at reflux for a few seconds, as all the solid dissolved. The mixture is chilled and the solid collected and washed with ether. The yield is 12.5 g. (74%), M.P. 274-7 C.

EXAMPLE G l-methyl-Z-p-tolypyrrolo [2,3-b] quinoxaline Sodium hydride (60% in mineral oil, 4.0 g., 1 mol.+ 100%) is placed in a flask fitted with a thermometer and a stirrer, and protected from atmospheric moisture. The mineral oil is removed by washing with tetrahydrofuran, followed by decantation. Dimethyl formamide (100 ml. is added, then 2-p-tolyl-1H-pyrrolo[2,3-b]quinoxaline 1s added in portions with stirring. When evolution of hydrogen gas has stopped, the flask is cooled in an ice-bath as methyl p-toluenesulfonate (9.05 g., 1 mol.) is added in portions, keeping the temperature below 20. The mixture is stirred for 4 hours at room temperature.

The mixture is diluted with ice and water, and the solid collected and well washed with water. After recrystallization from aqueous acetic acid, the yield is 7.45 g. (57%) M.P. 145-6 C.

EXAMPLE I 2-anilino-3-methylpyrazine hydro-p-toluenesulfonate NH-Ph osoioiru 9 cm A mixture of 51.5 g. (1 mol.) of 2-chloro-3-methylpyrazine and 150 g. (4 mols.) of aniline is heated at reflux for 1.5 hours. The mixture is cooled and added to 1 l. of a 10% aqueous potassium carbonate solution. The resultant mixture is extracted three times with 200 m1. portions of benzene. The combined organic phase is washed with water, dried by filtration through anhydrous magnesium sulfate, and distilled rapidly. The fraction, M.P. 136153 C./0.9 mm., is dissolved in 100 ml. of tetrahydrofuran and treated with a solution of excess p-toluenesulfonic acid in 50 ml. of tetrahydrofuran. The resulting solid is collected on a filter, washed with tetrahydrofuran and dried to give 113.8 g. (80%) of a yellow solid, M.P. 190-193 C.

22 EXAMPLE K 3-formyl-1-phenylpyrrolo[2,3 -b] pyrazine CHO I Ph

To a pre-formed complex of 11.5 ml. (3 mols.) phosphorus oxychloride in 40 m1. of dimethyl formamide is added 17.7 g. (1 mol.) of 2-anilino-3-methylpyrazine hydro p-toluenesulfonate. The resulting solution is heated on a steam bath for 3 hours then poured into 750 ml. of ice water. A 5 N aqueous sodium hydroxide solution is added portionwise until the solution is strongly basic and the resultant suspension is heated at 60 C. for 15 minutes. After chilling, the solid is collected on a filter, washed with water and dried. After recrystallization from isopropyl alcohol, 2.89 g. (27%) of product is obtained as a gray fibrous solid, M.P. -176 C.

By substituting other dye compounds of the invention, as defined in Formulas I and II above, into the procedure of the above examples, similar fogged, direct positive photographic silver halide emulsions and photographic elements may be prepared.

The photographic silver halide emulsion and other layers present in the photographic elements made accord ing to the invention can be hardened with any suitable hardener, including aldehyde hardeners such as formaldehyde, and mucochloric acid, aziridine hardeners, hardeners which are derivatives of dioxane, oxypolysaccharides such as oxy starch or oxy plant gums, and the like. The emulsion layers can also contain additional additives, particularly those known to be beneficial in photographic emulsions, including, for example, lubricating materials, stabilizers, speed increasing materials, absorbing dyes, plasticizers, and the like. These photographic emulsions can also contain in some cases additional spectral sensitizing dyes. Furthermore, these emulsions can contain color forming couplers or can be developed in solutions containing couplers or other color generating materials. Among the useful color formers are the monomeric and polymeric color formers, e.g., pyrazolone color formers, as well as phenolic, heterocyclic and open chain couplers having a reactive methylene group. The color forming couplers can be incorporated into the direct positive photographic silver halide emulsion using any suitable technique, e.g., techniques of the type shown in Jelley et al. US. Pat. 2,322,027, issued June 15, 1943, Fierke et al. US. Pat. 2,801,171, issued July 30, 1957, Fisher U.S. Pats. 1,055,155 and 1,102,028, issued Mar. 4, 1913, and June 30, 1914, respectively, and Wilmanns US. Pat. 2,186,849 issued J an. 9, 1940. They can also be developed using incorporated developers such as polyhydroxybenzenes, aminophenols, 3-pyrazolidones, and the like.

Although the invention has been described in considerable detail with particular reference to certain preferred embodiments thereof, it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove, and as defined in the appended claims.

We claim:

1. A cyanine dye selected from those represented by the following general formulas:

wherein n represents a positive integer of from 1 to 2; L represents a methine linkage; R represents a member selected from the group consisting of alkyl having from 1 to 4 carbon atoms, carboxyalkyl having from 3 to carbon atoms, sulfoalkyl having from 1 to 4 carbon atoms, hydroxyalkyl having from 1 to 4 carbon atoms, alkoxyalkyl having from 2 to 5 carbon atoms, an alkenyl group and a carbocyclic aryl group; R represents a member selected from the group consisting of an alkyl group having from 1-12 carbon atoms and a carbocyclic aryl group; R and R each taken individually represents a member selected from the group consisting of a hydrogen atom, an alkyl group having from 1-4 carbon atoms, and a carbocyclic aryl group; R and R taken together represent the non-metallic atoms necessary to complete a pyrrolo[2,3-b]quinoxaline nucleus; R represents a member selected from the group consistnig of a hydrogen atom and a carbocyclic aryl group; R represents a member selected from the group consisting of an alkyl group having from 1-4 carbon atoms, a carbocyclic aryl group and a heterocyclic radical containing from 5 to 6 atoms in the heterocyclic ring and having a hetero nitrogen, oxygen or sulfur atom; X represents an acid anion; D represents the non-metallic atoms necessary to complete a nucleus selected from the group consisting of a 2-arylindole nucleus, a pyrrolo[2,3-b]pyraziner nucleus and a pyrrolo[2,3-b]quinoxaline nucleus; and Z is selected from the group consisting of a nitrobenzothiazole nucleus, a, nitrobenzoxazole nucleus, at nitrobenzoselenazole nucleus, 9. nitroindole nucleus, an imidazo[4,5-b] quinoxaline nucleus, and a 1,3,3-trialkyl-3H-pyrrolo [2,3-b] pyridine nucleaus.

2. A cyanine dye selected from those comprising first and second nitrogen containing heterocyclic nuclei joined together by a dimethine linkage the first of said nuclei being selected from the group consisting of a l-alkyl or a l-aryl substituted pyrrolo[2,3-b]pyrazine nucleus and a l-alkyl or a l-aryl substituted pyrrolo[2,3-b] quinoxaline nucleus joined at the 3-carbon atom thereof to said linkage; and said second nucleus containing from 5 to 6 atoms and being selected from the group consisting of a nitrobenzothiazole nucleus, 3. nitrobenzoxazole nucleus, a nitrobenzoselenazole nucleus, a nitroindole nucleus, an imidazo[4,5-b]quinoxaline nucleus, and a 1,3,3-trialkyl-3H-pyrrolo[2,3-b]pyridine nucleus.

24 3. A cyanine dye selected from the group consisting of: 3'-ethyl 1 methyl-6'-nitro-2-p-tolyl-3-pyrrolo[2,3-b]

quinoxalinothiacarbocyanine p-toluenesulfouate;

1,3-dia1lyl 1' methyl-2'-p-tolylimidazo[4,5-b] quinoxalino-3' pyrrolo[2,3-b]quinoxalinocarbocyanine ptoluenesulfonate;

6-chloro-l'-methyl 1,3 diphenyl-Z'-p-tolylimidazo [4,5-b1quinoxalino 3'-pyrrolo[2,3-b1quinoxalinocarbocyanine p-toluenesulfonate;

1,1,3,3-tetramethyl 5 nitro-2'-p-tolylindo-3'-py1- rolo[2,3-b]quinoxalinocarbocyanine p toluenesulfonate; and,

1,l',3,3-tetramethyl 2 p-tolylpyrrolo[2,3-b]pyrido- 3'-pyrrolo[2,3-b]quinoxalinocarbocyanine perchlorate.

4. A cyanine dye selected from those comprising first and second nitrogen containing heterocyclic nuclei joined together by a trimethine linkage; the first of said nuclei being selected from the group consisting of a l-alkyl or l-aryl substituted pyrrolo[2,3-b]pyrazine nucleus and a l-alkyl or a l-aryl substituted pyrrolo[2,3-b]quinoxaline nucleus joined at the 3-carbon atom thereof to said linkage; and said second nucleus is selected from the group consisting of a 2-arylindole nucleus, at l-alkyl or a l-aryl substituted pyrrolo[2,3-b] quinoxaline nucleus and a l-alkyl or a l-aryl substituted pyrrolo[2,3-b'] pyrazine nucleus, each of said nuclei being joined at the 3-carbon atom thereof to said trimethine linkage.

5. A cyanine dye selected from the group consisting of:

3 indolo 3' pyrrolo[2,3-b]quinoxalinocarbocyanine bromide;

5,6-dimethyl 1,1-diphenyl-8-(3-pyridyl)-3 pyrrolo [2,3-b]pyrazino 3' pyrrolo[2,3-b]quinoxalinocarbocyanine bromide; 8-(2-fury1) l-methyl-1,2-diphenyl-3,i3'-pyrrolo[2,3-

bJquinoxalinocarbocyanine perchlorate;

8-ethyl-l'-methyl 5,6 diphenyl-3-pyrrolo[2,3-b]pyrazino-3 -pyrrolo [2,3-b] quinoxalinocarbocyanine bromide; and,

1,1-dimethyl-2,8-diphenyl 2' p-tolyl-3-indolo-3-pyrrolo[2,3-b]quinoxalinocarbocyanine perchlorate.

6. The cyanine dye 6-chloro-l'-methyl-1,3-dipheny1- 2'-p-tolylimidazo[4,5-b]quinoxalino 3 pyrrolo[2,3-b] quinoxalinocarbocyanine p-toluenesulfonate.

References Cited FOREIGN PATENTS 870,753 6/1961 England 260-240.6

JOHN D. RANDOLPH, Primary Examiner US. Cl. X.R. 

